The objective of the proposed research is to learn more about the mechanisms underlying both normal eye movement control and human ocular motor disorders. The research strategy is to make quantitative measurements of ocular motor function in both human beings and monkeys and to use control systems analysis to interpret the findings. Our major interest is in the mechanisms that maintain ocular motor accuracy with particular emphasis on problems peculiar to binocularity, eye muscle proprioception and the cerebellum. We will emphasize the study of adaptive mechanisms that improve binocular functions -- specifically the capability to make disconjugate, orbital-position dependent adjustments that compensate for asymmetrical muscle weakness. We will then use the models of unilateral ocular muscle palsy, prolonged monocular patching and spectacle correction for anisometropia to elicit and to characterize disconjugate ocular motor adaptation. Using techniques to open the vergence disparity feedback loop, we will also study vergence adaptation -- specifically using the initiation of vergence as a measure of vergence dynamics. To define the neurophysiological substrate of these adaptive mechanisms we will study the effects of interruption of ocular muscle proprioceptors and of lesions in the cerebellar flocculus -- the potential anatomical substrate(s) for disconjugate adaptation. Our results will provide new information about (1) disconjugate and vergence adaptive control and how they relate to disorders of ocular alignment such as paralytic and nonparalytic strabismus, (2) the function of ocular muscle proprioceptors, long a glaring unknown in ocular motor physiology and (3) the role of the cerebellum in ocular motor learning and plasticity specifically related to disorders of binocularity.